<!DOCTYPE html>
<html xmlns:th="https://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>


    <button th:text="#{System.title}">111</button>
    <button th:text="#{doc.my.name}"></button>

    <div class="dropdown-menu dropdown-menu-right" aria-labelledby="dropdownMenuButton">
        <a class="dropdown-item" th:href="@{/html(lang=es_ES)}">中文</a>
        <a class="dropdown-item" th:href="@{/html(lang=en_US)}">英语</a>
    </div>

</body>
</html>